THE MAKING OF A COMPOUND LEAF - GENETIC MANIPULATION OF LEAF ARCHITECTURE IN TOMATO

The most distinctive morphogenetic feature of leaves is their being ei ther simple or compound. To study the basis for this dichotomy, we hav e exploited the maize homeobox-containing Knotted-1 (Kn1) gene in conj unction with mutations that alter the tomato compound leaf. We show th at misexpression of Kn1 confers different phenotypes on simple and com pound leaves. Up to 2000 leaflets, organized in compound reiterated un its, are formed in tomato leaves expressing Kn1. In contrast, Kn1 indu ces leaf malformations but fails to elicit leaf ramification in plants with inherent simple leaves such as Arabidopsis or in tomato mutant p lants with simple leaves. Moreover, the tomato Kn1 ortholog, unlike th at of Arabidopsis, is expressed in the leaf primordia. Presumably, the two alternative leaf forms are conditioned by different developmental programs in the primary appendage that is common to all types of leav es.